Magnetic-Field-Induced Crossover to a Nonuniversal Regime in a Kondo Dot

TL;DR

This study investigates how magnetic field influences the Kondo peak splitting in a single-electron transistor, revealing a crossover from universal to nonuniversal behavior as magnetic field strength varies.

Contribution

It demonstrates that the magnetic splitting of the Kondo peak is not a universal function of the Kondo temperature, showing different behaviors at high and low magnetic fields.

Findings

At high magnetic fields, the splitting varies oppositely along different parameter paths.

At low magnetic fields, the splitting decreases with increasing Kondo temperature.

The ratio of splitting to Zeeman energy exceeds or falls below unity depending on magnetic field strength.

Abstract

We have measured the magnetic splitting, $\Delta_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $\Delta_K$ with $T_K$ along the two paths have opposite signs, indicating that $\Delta_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $\Delta_K$ with $T_K$ along both paths, in agreement with theoretical predictions. Furthermore, we find $\Delta_K/\Delta<1$ at low $B$ and $\Delta_K/\Delta>1$ at high $B$, where $\Delta$ is the Zeeman energy of the bare spin, in the same system.